1. Field of the Invention
This invention relates to semiconductor manufacturing, and more specifically to methods and apparatus for transporting wafer cassettes.
2. Background of the Related Art
Integrated circuit chips are usually formed on silicon wafers. Typically, the electrical and physical characteristics of these wafers are tested before chips are manufactured from the wafers. The testing is usually accomplished by a testing apparatus that sequentially tests wafers held in slots of a wafer cassette. The wafers are usually transported by production personnel between the various testing apparatus and manufacturing equipment in these wafer cassettes.
A typical problem in transporting wafers is particulate contamination. Even in industrial clean rooms, particles drift in the air and settle on wafers, degrading the quality of the wafers. Contaminant particles usually drift close to floor level, so that if wafers are transported at or above head level, much of the contamination on the wafers can be reduced.
There are several types of commercially available wafer cassette handles. The handles typically can be attached to a cassette for transport and then can be removed from the cassette when the cassette has been carried to a testing or destination area. The handles can be used to lift a cassette to or above head level during transport to reduce contamination.
A typical wafer cassette handle of the prior art is shown in FIG. 1a. The cassette handle 10 consists of attaching support 12 capable of engaging an edge of a wafer cassette, and a handle 14 extending away from the support 12. The support 12 includes L-shaped members 16a and 16b that engage grooves or flanges provided along an edge of a wafer cassette. Wafer cassette handles such as the one shown in FIG. 1a can be purchased from Fluoroware, located in Chaska, Minn., as model A055.
FIG. 1b shows the handle 10 attached to a typical wafer cassette 18. The cassette is approximately rectilinear and includes a number of parallel slots 19 to hold wafers in the interior of the cassette. The handle 10 is typically attached proximate a front face 22 of the cassette 18. The L-shaped members 16a and 16b engage slots 20a and 20b in the wafer cassette and the handle is moved upwardly from the bottom of the cassette along the front face 22 until they engage stops 24a and 24b, respectively.
FIG. 1c shows a production worker lifting the wafer cassette 18 by the handle 10. This holding position works for short, horizontal movement of the wafer cassette. However, if the cassette needs to be transported a relatively long distance, or if the cassette must be lifted vertically, this holding position can cause considerable wrist strain, as illustrated at 25. This strain can be a problem for operators who must transport many cassettes during a work day. The strain is worsened when the cassette is lifted to or above head level.
What is needed is a cassette handle that will allow a wafer cassette to be transported easily and with less strain than the previously-used handles. The cassettes should be able to be lifted and carried at a high level with little strain to reduce the particulate contamination on the wafers.